PARANOIA can make an octopus unsuitable for aquarium display, according to R C Anderson's report, 'Cephalopods at the Seattle Aquarium' in the 1987 International Zoo Yearbook. An emotional octopus may have to be excluded from tests for spatial awareness, according to J A Mather's paper 'Navigation by spatial memory and use of landmarks in octopuses' (Journal of Comparative Physiology, vol 168, 1991).

Such observations led Mather and Anderson to do more detailed studies on octopuses which they report in 'Personalities of Octopuses (Octopus rubescens)' in the Journal of Comparative Psychology (vol 107, no 3, 1993). The subjects were 44 one-year-old octopuses whose behaviours were recorded in three experimental states.

In the first, called 'alerting', the experimenter opened the lid of the tank and brought his head close so the octopus could see it; in the second, 'threat', the octopus was touched briefly with a test-tube brush; in the third, 'feeding', a crab was dropped into the tank.

19 modes of octopus behaviour were noted and scored. For example, in the 'feeding' state: 'For the capture technique, an octopus's behaviour was scored as 2 if the octopus made a jet- assisted leap through the water, as 1 if it walked along the aquarium bottom using the sucker- lined arms, and as 0 if it waited for capture until the crab walked up to it.'

Analysis of the observations revealed distinct individual differences between octopuses and led to the conclusion that octopuses do have personalities, with activity, emotionality and sociability the three main components. Further studies are proposed.